Present systems for producing products such as sodium chlorate by the electrolysis of sodium chloride solutions may generally be classified in the following groups:
A. Bipolar cells placed in large tanks. PA1 B. Small monopolar cells.
Both of these systems have inherent disabilities. The bipolar cells which are situated in a large tank of electrolyte, are generally swept with air to dilute the evolved hydrogen below the explosive limit, generally 50 volumes of air for each volume of hydrogen. This combined air-hydrogen stream contains small particles of sodium chloride and sodium chlorate, and because of the large volume involved it is very difficult to effectively scrub out these particles. Because of the configuration of the cells it is difficult to direct the air stream to obtain adequate contact between the air and the solution and to achieve sufficient evaporation which would result in cooling and concentration of the solution. For this reason large quantities of cooling water are needed and large expensive heat transfer surfaces are involved. Due to insufficient concentration of the solution this must be sent through an evaporator for further concentration prior to use in any of the standard chlorine dioxide generators. This requires more energy usually in the form of steam.
The small monopolar cells also have their inherent difficulties. Each small cell must have either its individual acid and electrolyte feed and individual cooling or the electrolyte from many cells must be circulated to a large reaction tank and heat exchanger. This, of course, requires extra equipment and energy for pumping. In this procedure no air is swept across the electrolyte to cause evaporation, cooling and concentration, therefore this system also requires large quantities of cooling water and large heat transfer surfaces and in addition the solution requires further concentration before it is suitable for chlorine dioxide generator feed.